Competing mortality and fracture risk assessment.

SUMMARY

Failure to account for competing mortality gave higher estimates of 10-year fracture probability than if appropriate adjustment is made for competing mortality, particularly among subgroups with higher mortality. A modified Kaplan-Meier method is easy to implement and provides an alternative approach to existing methods for competing mortality risk adjustment.

INTRODUCTION

A unique feature of FRAX(®) is that 10-year fracture probability accounts for mortality as a competing risk. We compared the effect of competing mortality adjustment on nonparametric and parametric methods of fracture probability estimation.

METHODS

The Manitoba Bone Mineral Density (BMD) database was used to identify men and women age ≥50 years with FRAX probabilities calculated using femoral neck BMD (N = 39,063). Fractures were assessed from administrative data (N = 2,543 with a major osteoporotic fracture, N = 549 with a hip fracture during mean 5.3 years follow-up).

RESULTS

The following subgroups with higher mortality were identified: men, age >80 years, high fracture probability, and presence of diabetes. Failure to account for competing mortality in these subgroups overestimated fracture probability by 16-56 % with the standard nonparametric (Kaplan-Meier) method and 15-29 % with the standard parametric (Cox) model. When the outcome was hip fractures, failure to account for competing mortality overestimated hip fracture probability by 18-36 % and 17-35 %, respectively. A simple modified Kaplan-Meier method showed very close agreement with methods that adjusted for competing mortality (within 2 %).

CONCLUSIONS

Failure to account for competing mortality risk gives considerably higher estimates of 10-year fracture probability than if adjustment is made for this competing risk.